Pneumatic tire having asymmetrical tread pattern

Abstract

Provided is a pneumatic tire capable of improving the drainage performance while favorably maintaining the uneven wear resistance. The pneumatic tire of the present invention is a pneumatic tire having a tread portion provided with at least three main grooves extending in a tire circumferential direction, these main grooves defining a plurality of land portions, the pneumatic tire characterized in that, when specified are a pair of the land portions positioned respectively at both sides of any one of the main grooves excluding the main grooves on outermost sides in a tire width direction, a plurality of first inclined grooves inclined to the tire circumferential direction are provided in one land portion of the pair of the land portions, and a plurality of second inclined grooves inclined in a same direction as that of the first inclined grooves are provided in the other land portion of the pair of the land portions, each of the first inclined grooves is opened at one end to the main groove positioned between the pair of the land portions, and is terminated at the other end in the one land portion, and each of the second inclined grooves is opened at one end to the main groove positioned between the pair of the land portions, and is terminated at the other end in the other land portion.

Description

TECHNICAL FIELD[0001]The present invention relates to a pneumatic tire including main grooves extending in a tire circumferential direction in a tread portion thereof. More specifically, the present invention relates to a pneumatic tire capable of achieving a good balance between drainage performance and uneven wear resistance.[0002]A pneumatic tire generally includes main grooves extending in a tire circumferential direction in a tread portion thereof. These main grooves have such a relatively large area that the drainage performance is guaranteed. Moreover, multiple lug grooves, extending in a tire width direction, are provided in the tread portion. When these lug grooves communicate with the main grooves, the drainage performance can be further increased.[0003]However, when land portions defined by the main grooves are partitioned into a number of blocks by lug grooves, there is a drawback that uneven wearing is likely to occur in these blocks. Against this, it is proposed that m...

AI Technical Summary

Benefits of technology

[0012]In the present invention, when specified are the pair of the land portions positioned respectively at both sides of any one of the main grooves excluding the main grooves on outermost sides in the tire width direction, the first inclined grooves having one end closed are provided in one land portion of the pair of the land portions, while the second inclined grooves having one end closed and inclined in a same direction as that of the first inclined grooves are provided in the other land portion of the pair of the land portions. In addition, each of the first inclined grooves and the second land portion is opened at one end to the common main groove positioned between the pair of the land portions. Such a main groove is positioned at a portion which is closer to a tire equator line than the main grooves on the outermost sides in the tire width direction are, and which has a relatively long footprint length in a tire circumferential direction. Accordingly, when the first inclined grooves and the second inclined grooves are communicated with the main groove, the drainage performance is effectively increased, while the uneven wear resistance is favorably maintained.

[0013]Here, it is preferable that an average inclination angle α of a profile line of the first inclined groove with respect to the tire circumferential direction, the profile line making an acute angle with an edge of the one land portion, and an average inclination angle β of a profile line of an second inclined groove with respect to the tire circumferential direction, the profile line making an acute angle with an edge of the other land portion, are 20° to 50°. By setting the average inclination angles α, β of the first inclined groove and the second inclined groove to be smaller than the respective upper limit values, the drainage performance is improved. Additionally, by setting the average inclination angles α, β to be greater than the respective lower limit values, the uneven wear resistance is improved.

[0014]An inclination angle of the profile line of the first inclined groove with respect to the tire circumferential direction gradually decreases from an opening end of the first inclined groove to at least a central position therein in a groove length direction, the profile line making an acute angle with the edge of the one land portion. In addition, an inclination angle of the profile line of the second inclined groove with respect to the tire circumferential direction gradually decreases from an opening end of the second inclined groove to at least a central position therein in a groove length direction, the profile line making an acute angle with the edge of the other land portion. Accordingly, a superb drainage performance is demonstrated.

[0015]A shortest distance γ1 to the first inclined groove from an edge on an opposite side of the one land portion to the edge where the first inclined groove is opened is 10% to 40% of a width of the one land portion. In addition, a shortest distance γ2 to the second inclined groove from an edge on an opposite side of the other land portion to the edge where the second inclined groove is opened is 10% to 40% of a width of the other land portion. By setting the shortest distances γ1, γ2 of the first inclined groove and the second inclined groove to be smaller than the respective upper limit values, the drainage performance is improved. Additionally, by setting the shortest distances γ1, γ2 to be greater than the respective lower limit values, the uneven wear resistance is improved.

[0016]Each of the land portions provided with the first inclined grooves or the second inclined grooves is preferably provided with multiple chamfered portions at the edge on an opposite side of the land portion to the edge where the first inclined groove or the second inclined grooves is opened. Accordingly, the uneven wear resistance is improved. Here, in order to obtain the effect of improving the uneven wear resistance sufficiently, it is preferable that: the maximum width of each of the chamfered portions be set to 10% to 30% of the width of the land portion; the maximum depth of the chamfered portion be set to 10% or more of the effective depth from a road-contacting surface to a wear indicator of the main groove; and the maximum width portion of the chamfered portion be disposed between a dead end of one of a pair of the inclined grooves neighboring in the tire circumferential direction and an opening end of the other of the pair.

[0017]Furthermore, in the present invention, attention has been focused on a pneumatic tire having an asymmetrical tread pattern with respect to both sides of a tire equator line, and designed to be mounted on a vehicle in a way that a designated side of the tire faces to an outside of the vehicle. The balance between the uneven wear resistance and the drainage performance is achieved by diligent combination of the mounting orientations and the arrangement of inclined grooves in such a pneumatic tire.

Problems solved by technology

However, when land portions defined by the main grooves are partitioned into a number of blocks by lug grooves, there is a drawback that uneven wearing is likely to occur in these blocks.

When such an inclined groove having one end closed is provided in an intermediate land portion positioned between a central land portion and a shoulder land portion, it is possible to suppress the occurrence of uneven wearing; however, the effect of improving the drainage performance is not always sufficiently obtained at present.

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